Ink jet printers provide a high degree of versatility with respect to print media and methods for printing multi-color images on print media. These advantages are due in part to the ability to design and provide relatively small printheads having multiple orifices which are in flow communication with an ink supply source or cartridge. In order to improve the quality and speed of ink jet printers, modifications to the printheads, including the use of smaller ink ejection orifices on permanent or semi-permanent printheads continues to evolve. Such printheads are often connected in flow communication with a replaceable ink jet cartridge.
Ink jet cartridges have widely varying design and may contain a capillary member or foam member for retaining ink and maintaining a predetermined back pressure on the ink so that the ink does not flow from the printhead onto the print media except when the ejectors on the printhead are activated. Other ink jet cartridges may contain a bellows or piston-like structure for maintaining ink back pressure in the cartridge. In such ink cartridges, the ink typically occupies a chamber within the cartridge.
Regardless of the means chosen for storing ink in an ink jet cartridge, if the cartridge is devoid of ink, misprinted pages may occur at an inopportune timer. In the worst case scenario, the printhead may be damaged by overheating in the absence of ink or by drying of ink in the passageways to the printheads.
U.S. Pat. No. 5,743,135 to Sayka et al. relates to a liquid level monitor which uses a tube to confine a float to a vertical path. The float is said to be a water filled stainless steel ball or cylinder which is detectable by a optical fiber which is connected to a photodetector. A light source such as a light emitting diode (LED) illuminates the float to provide transmittance or reflectance of light through the optical fiber to the photodetector. It is said that the float may have a fluorescent coating which can induce a frequency shift in reflected light to the source light to enhance detection where stray reflections are a problem.
Other methods for detection of ink levels include the use of prism inserts and an ink supply cartridge having a tank body optical ink level detection section to refract light at an angle with respect to the incident light when ink is present in the light path. Electrodes have also been used to detect the present or absence of ink in an ink container. An estimation of the ink remaining in an ink container may also be made by counting ink drops expelled from the printhead.
Methods for level detection have been proposed for various applications, such as reflecting light off the top surface of a liquid or off a bubble in the liquid. When the liquid is in a turbulent state, the light is said to be reflected from the top surface of the ink erratically. See U.S. Pat. No. 5,596,351 to Stapleton.
Of the foregoing methods, mechanical means for detection of ink level may be less reliable due to interference of a float in a vertical path for containing a float. Electrical means and optical means using prisms or ink tank inserts or special configurations are relatively expensive to implement and require a predetermined location for level detection with respect to an ink tank or cartridge which cannot be changed once the cartridge is manufactured.
There is a need for an ink level sensing device and apparatus which is less constrained with respect to the detection of ink level and which may be adaptable to a wide variety of ink cartridges without significantly changing the cartridge design.